CREATE EXTENSION osml10n CASCADE;
ERROR: extension "osml10n" is not available
DETAIL: Could not open extension control file "/usr/share/postgresql/15/extension/osml10n.control": No such file or directory.
HINT: The extension must first be installed on the system where PostgreSQL is running.
Why do you even think that there should be an PortgreSQL extension.
If you want to use the old deprecated code which does use an PortgreSQL extension look at:
https://github.com/giggls/mapnik-german-l10n
CREATE EXTENSION osml10n CASCADE; ERROR: extension "osml10n" is not available DETAIL: Could not open extension control file "/usr/share/postgresql/15/extension/osml10n.control": No such file or directory. HINT: The extension must first be installed on the system where PostgreSQL is running.